Cortical processing of sensory information plays a critical role in sensory discrimination, object recognition and memory. Cortical sensory processing has been shown to be highly dynamic, with past experience, current context and expectations shaping how the world is perceived on a moment by moment basis. Disorders of sensory processing constitute a major component of impairments induced by CNS disease and aging, as well as congenital disorders such as schizophrenia and autism. In the olfactory system, features of odorant molecules and mixtures are believed to be extracted by a large family of olfactory receptor proteins at the receptor sheet, and further defined by synaptic processing with the olfactory bulb. Current views of olfactory function suggest that re- assembly of these features into perceptual odor wholes is performed largely by circuits in the primary olfactory cortex. Work completed during the past funding period of this award provided evidence that odor encoding by piriform cortical neurons is highly dynamic, and appears to be consistent with the experience-dependent synthetic role proposed for this cortex. In addition, evidence was obtained suggesting that anterior piriform cortex neural ensembles encode odor identity, while posterior piriform cortical ensembles encode odor quality. Experience-dependent object encoding and perception in neocortical sensory systems is heavily dependent on intrinsic, intracortical association fibers. A similar, highly plastic intrinsic association system exists in the piriform cortex, and in fact dominates dendritic trees in posterior piriform compared to anterior. The present proposal examines the role of the piriform cortical intrinsic fiber system in odor encoding and perception using single-unit, multiple single-unit and behavioral techniques. Aim 1 proposes to parametrically examine how needs for a balance between pattern completion (generalization between slight variance within an otherwise constant stimulus) and pattern separation (discrimination of similar odors) are met in piriform cortex and translated to behavior, Aim 2 proposes to further examine the effects of experience on pattern completion and separation in anterior and posterior piriform cortex, and Aim 3 proposes to examine odor experience-induced plasticity of intrinsic cortical connections and their role of cortical ensemble formation and odor discrimination. Information processing by cortical networks is critical for normal sensory perception, memory, and motor responses to the environment. Understanding how information is entered into, and analyzed by these networks will have a fundamental impact on our ability to interpret and treat disorders of these basic cognitive functions. This proposal takes advantage of the relatively simple organization of the olfactory system and its robust plasticity to examine how sensory experience modifies cortical circuit function.